1. Field of the Invention
The present invention relates to a processing method of the outermost periphery edge of silicon wafer, more in detail relates to a mirror finishing method of chamfered outermost periphery edge of silicon wafer by a plasma etching method and an apparatus for mirror finishing by plasma etching.
2. Description of the Prior Art
Electric parts such as IC, LSI, or VLSI which are made from semiconductor materials e.g. silicon mono crystalline are produced as follows. That is, an ingot of silicon mono crystalline compound semiconductor is sliced to a thin wafer, precise electrical circuit pattern is formed on the surface of wafer and divided to chips. At the processing of silicon wafer, which is a starting material of these electric parts, the outermost periphery of wafer is chamfered to have obtuse angles or an arc profile and mirror finished as well as the surface of wafer not to be chipped and not to enfold fine particles of dust. Especially, from the view point of a tendency to smaller size and larger integration of these electric parts, or along with the rapid progress of epitaxial technique, more precise surface roughness is becoming to be required not only on the surface of silicon wafer but also on the outermost periphery edge of silicon wafer.
An as cut wafer which is prepared by slicing an ingot is lapped, etched and polished as to processed to a mirror finished wafer at least one side is mirror finished. On the mirror finished surface, fine and precise electrical pattern is formed at the device process. The wafer is processed maintaining the original disk shape until it is divided to unit semiconductor chips between above mentioned main processes, there are washing, drying and transporting processes. If the outermost periphery of the wafer has steep and sharp edge and coarser surface roughness during above mentioned series of processes, the sharp edge contacts with an apparatus or other substance and very fine particles are generated by very small breaking. Further, very fine contamination particles are caught in the coarse surface of edge, and the enfolded fine contamination particles are released at, the latter process and cause the contamination problem of the precise finished surface, which deteriorate the yield of products and the surface quality. Usually, to prevent above mentioned problem, the outermost periphery edge of the wafer is chamfered and mirror finished at, the early stage of the wafer processing.
In general, the above mentioned edge polishing is carried out, by following method. Namely, the outermost periphery edge of the wafer is chamfered using beveling grinding stone containing diamond abrasives, then the chamfered edge is polished by an edge polishing machine which is disclosed, for example, in Japanese Patent Laid Open Publication 64-71656 or Japanese Patent Laid Open Publication 1-171656. Said edge polishing machine uses polishing pad and slurry containing abrasives and the polishing is carried out in wet condition. According to these type of machine, the edge polishing process is very complicated and takes long time, further scratches by diamond abrasive can not be removed perfectly and remain on the surface of outermost periphery edge. The depth of remained scratches is shallower than as chamfered wafer, however, still have a tendency to enfold fine contamination particles. The requirement for improvement of this point is becoming more severe along with the progress of the tendency to smaller size and larger integration of IC, LSI or VLSI, and the required precision for silicon wafer processing becomes more strict.
Since said conventional method is based on wet condition, the load to wasted water treating facilities is relatively high, further it is pointed out as the problem that the setting up of the preparing apparatus for DI water which is necessary for the edge polishing is necessary. Further, when the edge polishing is carried out after the surface polishing of the wafer, since slurry, fine fluff of polishing pad or fine debris of silicon wafer are stuck to the mirror finished surface of wafer and contaminate the mirror finished surface, it is necessary to set up another washing process. And said contamination causes new stains or scratches, therefore said conventional method can not be said as a sufficient, method.
In the meanwhile, as the method to process the wafer surface in dry condition, the method by plasma etching is proposed for instance in Japanese Patents Laid open Publication 9-115887. In said method a wafer is transferred to the horizontal direction and the surface is processed partially and whole surface is processed gradually, thus the planarization of whole wafer surface can be accomplished. By this method, since D.I water is not needed and does not, generate waste water, a clean processing Without environmental contamination can be possible. However, up to the present, said plasma etching method is limited only to the surface processing.
The inventors of this invention have carried out an intensive study to dissolve the problem of surface roughness at the edge polishing of the outermost periphery of silicon wafer along with the improvement of processing accuracy of silicon wafer, and find out that, by polishing the outermost periphery edge of silicon wafer using a plasma etching method disclosed in said Japanese Patent Laid open Publication 9115887, desired fine mirror finished edge surface can be obtained and accomplished present invention. The object of this invention is to provide a mirror finishing method by plasma etching of the outermost periphery of silicon wafer, and another object of this invention is to provide an apparatus for mirror finishing by plasma etching apparatus.
The above mentioned object can be accomplished by a silicon wafer processing method comprising, etching the outermost periphery edge of silicon wafer by activated species gas generated in plasma. Said activated species gas generated in plasma can be produced for example by dissociation of sulfur hexafluoride gas in a discharge tube. And another object of this invention can be accomplished by a plasma etching polishing apparatus for outermost periphery edge of silicon wafer comprising a means to hold and rotate a silicon wafer, a container which cover all surface of silicon wafer except a part of outermost periphery edge, a vacuum chamber which contain said container and a plasma generating means. In said plasma etching polishing apparatus for outermost periphery edge of silicon wafer, it is desirable that the inside of the container which cover all surface of silicon wafer except a part of outermost periphery edge is maintained at positive pressure condition by nitrogen gas or inert gas.
The rough surface of silicon wafer is averaged by the irradiation of plasma activated species gas, and a precise surface corresponding to a polished surface can be obtained. The polishing of outermost periphery edge of silicon wafer can be carried out by containing a silicon wafer in a container which covers all surface of silicon wafer except, a part of outermost periphery edge, maintaining the inside of container at, plus pressure condition by nitrogen gas or inert gas, then irradiating whole outermost periphery edge of silicon wafer by plasma activated species gas rotating said silicon wafer,